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Bizarre green meteorite NWA 7325 may be from Mercury

Wow, that’s what I call green! Green, glassy fusion crust coats one side of Ralew’s new meteorite. This is the largest of the 35 fragments, weighing just over 100g. Cube at right is 1 cm across. Click for larger version. Credit: Stefan Ralew

In April 2012 Stefan Ralew, a meteorite collector from Berlin, found himself staring at a spread of 35 green meteorite fragments for sale by a dealer in Morocco

“It was offered as a Martian (meteorite) but for me it was simply far too green,” said Ralew. Moroccan meteorite always keep an eye out for green rocks in the belief that they’re of Martian origin. Sometimes however they turn out to be nothing more than Earth rocks. Since this one was expensive, Ralew would have normally declined, but he noticed that the pieces had fusion crust, that frothy, typically dark coating of melted rock that forms when a meteorite is heated during its fall through the atmosphere.

Stefan Ralew Credit: Mirko Graul

“It was a big risk because of the high price,” said Ralew, but he sealed the deal and mailed off a piece to Dr. Tony Irvingat the University of Washington, well-known for his expertise in meteorites from other planets.

After chemical analysis, Irving discovered that Ralew’s green rock was a completely new type of achrondrite (ay-KON-drite), a class of igneous meteorite that forms deep within the crust of larger asteroids and planet-sized bodies. In fact, Ralew’s green meteorite shared similarities with the planet Mercury, making it a one-of-a-kind.

Many of the more familiar achondrites that scientists and meteorite hunters have picked up here on Earth were blasted from the surface of Vesta by meteorite and asteroid impacts. Still others have been liberated from the moon and Mars. They drift through space until swept up by the ceaseless Earth. Scientists have done the math and arrived at the conclusion that meteorites from Mercury impacts should also by lying around in the deserts of the world, preserved by arid air and lack of rain. But no one had definitely identified a rock from Mercury until the green meteorite entered the scene.

A closeup of a polished, cut face of NWA 7325 shows striking green crystals of chromium diopside (a silicate mineral with chromium) and gray crystals of plagioclase, a rock also common in Earth’s crust. Click for larger version. There are a total of 345 grams (about 12 ounces) mostly in small fragments. Credit: Stephan Ralew

Other classes of achondrites called aubrites and angrites were once believed to have originated on the innermost planet, but further research points to their home on a yet-unknown asteroid or planet.

Mercury photographed by MESSENGER. The planet’s crust lacks iron and is pockmarked by countless craters. One of these impacts possibly sent NWA 7325 our way. Credit: NASA

Stefan’s meteorite, now classified as NWA 7325 (NWA=Northwest Africa, its find location), is a near-match for rocks examined from orbit by Mercury MESSENGER space probe. NWA 7325 is rich in magnesium, calcium and a silicate material laced with chromium that lends it an emerald sparkle, but it lacks iron. And that’s the key. Surface rocks on Mercury are likewise igneous and depleted in iron.

The match isn’t perfect. NWA 7325 has more calcium than it should and lacks the silicate mineral enstatite (common on Mercury), but that doesn’t worry scientists too much. Because the rock was excavated from deeper down in the crust, it would be expected to have its own unique qualities.

Mars meteorites show evidence of shock from impact in their crystal structures, and the same would be expected for rocks delivered to us from Mercury. Plagioclase, a very common mineral in Earth’s crust, and found in abundance in NWA 7325, has been completely melted, likely due to shock from the impact that sent it flying from the planet long ago.

While the evidence points to a Mercury origin, we won’t really know for certain whether Ralew’s rock originated from the innermost planet until further studies are done. Scientists are still working to determinewhen those gorgeous green crystals formed as well as how long the rock coasted through space before arriving on Earth.

“Ultimately, only a sample return from Mercury may provide an answer,” wrote Irving in his group’s recent report on NWA 7325. In the meantime, Stefan’s meteorite stands as one of the most singular finds to date. It couldn’t have happened to a better guy. Ralew has a been a great friend of meteorite collectors and the scientific community for years. You can check out his website HERE.

About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

H.Bob,
The fact that it’s a one of a kind makes it rather spectacularly valuable. Stefan does plan to make some available to the collecting community but I daresay I’ll need another job to afford a piece.

So is that because Venus has so much atmosphere (both in depth and in density)? I’m guessing it would take something the size of a small planet to actually knock pieces of Venus far enough and fast enough out into space to escape the gravity of Venus and eventually become a meteorite on Earth. The impacting body would have to be big enough to survive the trip down through that atmosphere and still have enough ‘punch’ to push pieces of Venus back out through that same atmosphere and into space at an escape velocity. Mind you, I suppose that if this meteorite in your post is actually rock that originated on Mercury, then it had to have been hit pretty hard too since it traveled a very long way against the gravity of the Sun!

Thanks for your reply and for the link to the information. I don’t know much about the minerals that are described but it mentions that eskolaite is rare. Is that what indicates that it’s origin is planet mercury? The picture at the top of the page makes it look yellow also.

I am having difficulty, believing this, (from an Australian newspaper).
“Scientists believe the first chunk of planet Mercury has landed on Earth.” (AAP). Which scientists? The facts, known to any amateur, not, it seems, to ‘scientists’:
Mercury is exceptional in having a live planetary magnetic field – perhaps only one hundredth the ‘strength’ of Earth’s, but, unlike Venus, Mars, and asteroids, it has a field. Remnant magnetism lingers in the rock of some bodies such as the moon and Mars. Venus does not have any measured magnetism as a planet and pieces of Venus have not been identified as meteorites.
NWA 7325 by the ‘scientist’s’ own admission, is exceptionally depleted in iron. A piece of rock coming from an exceptionally iron –poor region may (or may not) happen to be magnetically distinct, as a product of its environment. Subsequent events, such as impact shock and space travel, might also influence magnetic property.
Meanwhile, the chemistry does not entirely match what is known of Mercury – no problem, bury it a bit. It can still be Mercury.
Why not bury the thing in Venus?
What are these people talking about? What is AAP talking about?
Anyone with an interest in the significance of this green meteorite might GOOGLE under, “Significance NWA 7325 lunar origin waterway woodlands Texas”.
Someone got bogged in a Texas swamp in the woods, and moonshine may be implicated?

lot of people talk about the price .and many of them are confused .i think that when meteorite is ungrouped it depends on it can be cheap or it can be expensive but i think that some times ppl are exaggerating the prices

Hello, I’m not very good with rocks but I have found some various sized rocks which has what appears to be melted green glass mixed around other round half melted inclusions with a smooth surface. The rock is not magnetic and does have small melted glass like red inclusions. Did you get a chemical signature of this sample mentioned? You have any idea where one can find out what type of rock this maybe? Thanks for your time and consideration

Hi Jimmy,
Very hard to say what you have but it’s unlikely you’d come across a relative of this meteorite because it’s extraordinarily rare. You can send me a photo at rking@duluthnews.com if you’d like. Here’s the mineralogical description of what’s in NWA 7325: http://bit.ly/WIZKRS

I have a large rock that looks very similar to the ones posted above. I found it six years ago and have yet to identify its origin. I believe that the rock I have contains quite a bit of iron which differs from what is described above. I suppose I am curious if there is anyone who may be willing to try to identify this rock or if anyone has any suggestions.

I found what I believe to be a very similar meteor while metal detecting,which is why I happened on to this site. Actually I have two, the smaller of the two has very little of the green on it that one is 209 grams. The other is over 500 grams in weight. It would have been nice if I could have posted a picture.